Solar System Log by Andrew Wilson, published 1987 by Jane's Publishing Co. Ltd.

The Soviets decided to send this next 7K-L1 spacecraft, not on a circumlunar flight, but about 330,000 kilometers into deep space in the opposite direction of the Moon in order to test the main spacecraft systems without the perturbing effects of the Moon (much like the Surveyor model test flights in 1965 and 1966).

The spacecraft was successfully boosted on its trajectory and reached an apogee of 354,000 kilometers. During the flight, although a key attitude-control sensor worked only intermittently, controllers managed to aim the spacecraft for a guided reentry back into Earth's atmosphere. Unfortunately, the same sensor failed at reentry, preventing the vehicle from maintaining stable orientation. Instead, Zond 4 began to carry out a direct ballistic reentry for landing in the Indian Ocean. An emergency destruct system, however, destroyed the returning capsule over the Gulf of Guinea to prevent foreign observers from recovering the wayward spacecraft.

Key Dates

2 Mar 1968: Launch

Status: Partial Success

Fast Facts

Zond 4 was an engineering test in support of the Soviet lunar exploration program.

It was sent into space in the opposite direction of the Moon to test systems without lunar interference.

Two cosmonauts in an isolated bunker communicated with the flight-control center via a relay onboard the spacecraft to simulate communication between cosmonauts in space and controllers on Earth.